Diffusion vacuum pumps



K'. VERFUSS DIFFUSION VACUUM 4 PUMPS Jan. 9', 1968 2 Sheets-Sheet l Filed Nov. y 29, 1965 Jan. 9, 1968. K, VERFUSS 3,362,621

l DIFFUSION VACUUMPUMPS Filed Nov. 29, 1965 2 Sheets-Sheet 2' l//lIlI/I/fllllll Maw Vor/i255 y We. WW.,

United States Patent 9 ciaims. (ci. 23o-nn) ABSTRACT F THE DISCLOSURE A four stage jet nozzle assembly for a diffusion pump having a cylindrical housing, includes a cylindrical thin walled base member having an inwardly projecting annular rib for supporting a central support member. The support member includes Vertical walls which dene a central column and four projecting walls in oruciform arrangement. Progressing from the bottom towards the top of the sup-port member, the edges of the projecting walls `define vertical segments which extend furtherest from the central column at the base, and are progressively nearer the central column moving toward the top. An annular ring is secured to the outermost vertical segments at the base of the support member; and this ring is dimensioned for a press lit with the base member and to rest on the annular rib. Similar rings are secured =to other segments. Each of the nozzles for the diffusion pump is formed by a lower -cylindrical wall portion and an upper outwardly and downwardly flared cap portion, the two portions being appropriately spaced vertically. To d'ene the nozzle mouth for the lowermost stage, the lower wall portion is formed rby the upper periphery of the base member. Positioned immediately above the base member is an annular member, which consists of an upper cylindrical portion and a lower outwardly flared portion; the lower outwardly flared portion defining the cap portion of the lowermost stage nozzle, and the cylindrical portion forming the lower portion of the nozzle for the adjacent stage. The cylindrical wall portion is press fit on an annular ring of the support member; and this member is vertically positioned during assembly relative to the base member to fix the nozzle mouth gap for the lowermost stage. Second and third annular members of progressively lesser diameter, each including a lower flared portion and an upper cylindrical portion are similarly mounted on the support member, to define the nozzles of succeeding stages, progressing upwardly. The cylindrical portion of the uppermost annular member defines the lower portion of the top stage; and an associated cap member is secured to the top of the support member. Additionally, annular, downwardly concave nozzle deflectors are separately supported on the support member. This structure provides for ease of fabrication and assembly of a nozzle assembly for a diffusion pump; wherein the vertical gaps of the four nozzles may be adjusted in assembly, eliminating critical tolerances in manufacture.

This invention relates generally to diffusion vacuum pumps and more particularly to improved jet assemblies for such pumps.

The operation of diffusion vacuum pumps is generally well known. A pumping fluid is evaporated in a heated boiler of the pump and the resulting vapor is directed at supersonic velocity through a jet assembly nozzle system to be finally condensed on a cold surface. As the high speed vapor stream passes between the nozzle system and the condensing surface, it accepts by diffusion gas molecules from an enclosure being evacuated and ICC compresses these molecules into a higher pressure region which normally communicates with a mechanical backing pump. The condensate produced on the condensing surface returns to the pump boiler for reheating and reevaporation.

Most commercial diffusion vacuum pumps are multistage devices which include a plurality of vertically stacked jet assemblies. As described in co-pending U.S. application No. 478,338 assigned to the assignee of the present invention, now Patent No. 3,342,405 issued Sept. i9, 1967, various dimensions of the individual jet assemblies are inter-related and critically alfect pump performance. Thus, to obtain satisfactory performance characteristics extremely close dimensional tolerances must be maintained during the production of a pump. Accordingly the manufacturing costs of conventional diffusion vacuum pumps are relatively high.

The object of this invention is to provide an improved diffusion vacuum pump which exhibits high performance characteristics and substantially reduced manufacturing cost.

One feature of this invention is the provision of a diffusion vacuum pump having a plurality of vertically spaced annular jet assemblies supported by a central column and wherein, in the regions of contact between the annular jet assemblies and the central column, the inner dimensions of the jet assemblies are greater than the outer dimensions of the central column. This structure permits vertical adjustment of the jets during assembly and eliminates the requirement for close vertical tolerances during manufacture of the individual components.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured type wherein the jet assemblies include annular nozzle bases and annular nozzle caps vertically spaced to form nozzle mouths, and wherein the nozzle bases and nozzle caps are individually supported by the central column. This structure permits relative vertical adjustment between the nozzle parts to establish desired gap widths for the nozzle mouths.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured types wherein the jet assemblies include nozzle deflectors formed by flexible, annular members supported at their inner edges by the central column and having their outer peripheries flexed' into a downwardly concave form by Contact with the inner surfaces of the nozzle caps.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured types wherein the jet cap of at least one jet assembly and the jet base of the immediately above jet assembly are formed by a commonly supported unitary structure.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured types wherein the central column includes laterally extending arms having terminal portions which provide support surfaces for the annular jet assemblies.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured types wherein the terminal portions of the laterally extending arms form annularbraces which support the jet assemblies.

Another feature of this invention is the provision of a diffusion vacuum pump of the above feature types wherein the annular jet assemblies have inner dimensions substantially equal to the outer dimensions of the lateral support arms terminal portions thereby insuring a closet Contact therebetween.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured type wherein the terminal portions of the lateral support arms form circular rings having outer diameters substan- 3, 3 tially equal to the inner diameters of the annular jet assemblies.

Another feature of this invention is the provision of a diffusion vacuum pump of the above featured type wherein the inner dimensions of the individual jet assemblies and the corresponding outer dimensions of the central support decrease for adjacent jet assemblies taken consecutively, upwardly. This structure allows passage of the individual jet assemblies over the central column during assembly of the pump.

These and other features and objects of the present invention will become more apparent upon a perusal of the following specification taken in conjunction with the accompanying drawings wherein.

FIG. 1 is an elevation view, partially in cross-section, of a preferred embodiment of the invention;

FIG. 2 is a cross-section taken on the line 2-2 of FIG. l; and

FIG. 3 is a cross-section taken on the line 3 3 of FIG. 1.

Referring now to FIGS. 1 and 2 there is shown the cylindrical pump casing 11 having an open top end 12. The mounting flange 13 surrounds the top end 12 and is adapted for connection to an enclosure (not shown) to be evacuated.

Mounted within the pump casing 11 is the central support 14 including the circularly cylindrical base 1S which rests on the bottom of the pump casing 11 and supports the central column 16. Extending laterally from the central column 16 are the perpendicular arm members 17 which support the vertically stacked jet assemblies 18, 19, 20 and 21.

Each of the jet assemblies is formed by a nozzle base 22 spaced from a nozzle cap 23 to form an annular nozzle mouth 24. The nozzle bases of the upper jet assemblies 19, 20 and 21 are circularly cylindrical in `form and have conically flared lower portions which form the nozzle caps 23 of the lower jet assemblies 18, 19 and 20. Secured to the central column 16 by the threaded screw 26 is the conically shaped nozzle cap 25 of the jet assembly 21. The bottom nozzle base 22 is formed by the upper portion of the support base 15.

The support arms 17 have longitudinal segments of varying lateral width. These lateral widths decrease in an upward direction so as to accommodate the diminishing circumferences of the individual jet assemblies 18, 19, 20 and 21. The terminal portions 31 of the uppermost vertical segments establish a circle having a diameter substantially equal to the inner diameter of the circularly cylindrical nozzle base of the top jet assembly 21. The next lower segments of the support arms 17 terminate in a circular brace 32 having an outer diameter substantially equal to the inner diameter of the cylindrical nozzle base of the jet assembly 20. Similarly, the next lower segments of the support arms 17 terminates in a circular brace 33 having an outer diameter substantially equal to the inner diameter of the cylindrical nozzle base of the jet assembly 19. Finally, the bottom longitudinal segments of the support arms 17 terminate in the circular brace 34 having an outer diameter substantially equal to the inner diameter of cylindrical nozzle base of the bottom jet assembly 18.

The middle jet assemblies 19 and 2t) include the annular nozzle detlectors 3S which have circularly cylindrical lower portions 39 and outwardly flared upper portions which provide downwardly facing concave surfaces 41. Supporting the nozzle deflectors 38 are the circular rings 42 formed by intermediate terminal portions of the support arms 17. The rings 42 have cuter diameters substantially equal to the inner diameters of the deflector lower portions 39. A widened bottom edge 43 of the ring 33 forms a concave deflector surface for the bottom jet assembly 18.

During assembly of the pump, the brace 3ft of the central support 14 is press fitted into the cylindrical base 15 until contact is established with the annular groove 48 therein. The nozzle base 22 for jet assembly 19 (preferably made of a relatively thin walled metal) is then passed over the top of the central support 14 and press fitted upon the circular brace 33. The dimensional relationship between the cylindrical nozzle base 22 and the circular brace 33 permits vertical adjustment of the jet assembly relative to the central support 14 and establishment of a desired gap width for the nozzle mouth 24 of bottom jet assembly 18. After the adjustment has been made the press fit contact between the components maintains their relative position. If desired, a few spot welds can be made to further stabilize the desired vertical re lationship between these elements. The nozzle deflector 33 is then passed over the top of central support 14 and press fitted upon the circular brace 42. The vertical po sition of the detiector plate 38 is established by contact of the groove 51 with the upper surface of the brace 42.

Subsequently, the cylindrical nozzle base 22 of the jet assembly Ztl is passed over the top of the central support 14 and press fitted upon the circular brace 32. Dur ing this operation, the inner surface of the integral noz zle cap 23 for the jet assembly 19 engages the outer pe riphery of the dellector 38 flexing it into the downwardly concave form 41. The vertical position of the jet as sembly is established as above to provide the desired nozzle mouth gap width for the third stage jet assembly 19.

The mounting and adjustment of the nozzle deector 38 for the second stage jet assembly 20 and the nozzle base 22 of first stage jet assembly 21 proceeds in the manner described above. Securement of the nozzle cap 25 for the top jet assembly 21 is accomplished with the mounting screw 25. Finally, the entire assembly is inserted into the pump casing 11.

It will be obvious that the structure described eliminates many of the close production tolerances required for the manufacture of conventional diffusion vacuum pumps. Since vertical adjustment of the individual stages can be made during assembly the requirement of close vertical tolerances is substantially eliminated. Similarly, the tiexible deflectors 3S are very inexpensive components which can be produced without the costly machining or close tolerance casting required with conventional pumps.

During operation of the pump, hot pumping fluid vapor which has been heated in the pump boiler located in .the lower portion of the pump housing 11 rises through the jet assembly between the perpendicular support arms 17. A certain portion of the rising vapor is intercepted by each of the vapor deflectors 38 and 43 and is directed through the nozzle mouths 24 of the lower three stages. The remaining vapor continues upward and is directed by the top nozzle cap 25 through the mouth 24 of the first stage jet assembly 21. The escaping vapor is then condensed on the cold inner surface of the pump casing 11 which is cooled by suitable cooling devices (not shown). The condensate formed runs down the inner surface of the pump casing 11 under the inuence of gravity and returns to the pump boiler for reheating and reevaporation. As the high speed vapor stream passes between the nozzle mouth and the condensing surface it accepts and compresses gas molecules downwardly. These molecules are pumped out of the outlet port 51 by a mechanical forepump (not shown).

Thus the present invention provides an improved diffusion vacuum pump which is capable of a relatively high pumping performance but which greatly reduces the complexities and intricacies of pump production. Accordingly, manufacturing costs are substantially reduced.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention can be practiced otherwise than as specifically described.

What is claimed is:

1. A diffusion vacuum pump comprising a housing; a support member mounted within said housing, including a central column and arms extending laterally therefrom; a plurality of vertically spaced annular nozzle assemblies surrounding and supported by said support member, each nozzle assembly including an annular base and an annular cap to define an annular nozzle mouth; said nozzle bases and nozzle caps being supported individually by said support member;

characterized in that the terminal portions of said laterally extending arms provide support surfaces for said annular nozzle assemblies; and said arms being dimensioned relative to the inner dimensions of said annular nozzle assemblies, in the regions of support contact therewith, to permit relative vertical movement therebetween during assembly whereby the nozzle mouth gaps may be established.

2. A diffusion vacuum pump according to claim 1:

characterized in that the terminal portions of said laterally extending arms comprise annular braces which define said support surfaces.

3. A diffusion vacuum pump as set forth in claim 2:

characterized in that the inner dimensions of the several annular nozzle assemblies and the corresponding outer dimensions of the respective support surfaces of said Support member, decrease for adjacent nozzle assemblies progressing consecutively upward.

4. A diffusion vacuum pump as set forth in claim 1:

characterized in that the annular nozzle cap of at least one nozzle assembly and the annular nozzle base of an adjacent nozzle assembly are formed by a single annular structure surrounding and supported by said support member.

5. A diffusion vacuum pump as set forth in claim 1:

characterized in that the inner surfaces of said annular nozzle assemblies are cylindrical; said support surfaces of said support member arms defining cylindrical surfaces; and the diameters of said inner cylindrical surfaces of said nozzle assemblies and said cylindrical surfaces defined by said support surfaces being substantially equal to provide a close fit contact between said surfaces.

6. A diffusion vacuum pump as set forth in claim 2: characterized in that the inner surfaces of said arcuate nozzle assemblies and the outer support surfaces of respective annular bases are cylindrical surfaces; and 5 each pair of mating cylindrical surfaces having substantially equal diameters thereby providing a close fit contact therebetween.

7. A diffusion vacuum pump as set forth in claim 5:

characterized in that said mating cylindrical surfaces are dimensioned for a press fit.

8. A diffusion vacuum pump comprising a housing; a support member mounted within said housing; a plurality of vertically spaced annular nozzle assemblies surrounding and supported by said support member, each nozzle assembly including an annular base and an annular cap to define an annular nozzle mouth; said nozzle bases and nozzle caps being supported individually by said support member; said support member being dimensioned relative to the inner dimensions of said annular nozzle assemblies, in the regions of support contact therewith, to permit relative vertical movement therebetween during assembly:

characterized in that said annular nozzle assemblies include annular nozzle defiectors, said nozzle defiectors surounding and being individually supported by said support member; and said nozzle defiectors having downwardly facing concave surfaces adapted to deect pumping fluid vapor through said nozzle mouths.

9. A diffusion vacuum pump as set forth in claim 8:

characterized in that said annular nozzle deectors are exible members supported at their inner edges by said support member and having their outer peripheries in flexing contact with the inner surfaces of said nozzle caps.

References Cited UNITED STATES PATENTS 1/1963 Stevenson 230-101 1/1965 Landfors 230-101 5/1965 Bachlen 230-101 

